The invention relates to seismology. In one aspect, the invention relates to an apparatus usefully employed to detect seismic phenomenon. In another aspect, the invention relates to a method for positioning an apparatus for the detection of seismic phenomenon.
The "seismic signal" is the sound that is initiated at the surface and propagates into the earth. It is distinguished from the "seismic response" that is reflected to the surface. The signal sound is characterized by the source producing it. It can be measured by putting a geophone near the source and recording the sound as it leaves. This recording is called the "signature" of that source. The signature shows what wavelet was introduced into the ground, whereas the record section shows what wavelet is returned to the surface. The source signature signal which propagates into the earth is not the same as the geophone response signal which returns, after being filtered by the earth.
The main importance of the seismic signature is in its use to improve the quality of recorded seismic data. Since the source signature is the signal that is propagated into the earth, neglecting attenuation effects, any reflecting horizon returns the entire wavelet. A seismic record that is made up of reflections has many overlapping reflections.
Further, it is typical that the seismic sources operate at locations having topography that is at variance with the topography of other survey sites. Therefore, the energy pulses transmitted into the strata by the seismic sources are frequently at variance with one another, and the resulting reflections will correspondingly exhibit dissimilar wave form characteristics.
Deconvolution is a mathematical process for partly recompressing the stretched-out wavelets into shorter ones. The trace is processed with an operator, another trace, that, when combined with the first, has the effect of reducing repetitions in the trace. The extra legs of a wavelet are reduced or eliminated, so a reflection is not so likely to interfere with a following one. The reflections can then be better distinguished as separate events.
Signature deconvolution is a powerful tool for data enhancement. It can be used where the signature of the source has been recorded. The source signature is used to aid in the selection of the best operator. The result is a deconvolution process which produces better processed data.